1. Field of the Invention
The present invention relates to semiconductor packages and, more specifically, to semiconductor packages of the stud type.
2Description of the Related Art
FIG. 1 is a fragmentary side view of a conventional stud-type semiconductor package. Referring to FIG. 1, a copper stud 1 is threaded into and fixed to a heat sink portion (not shown) as a heat dissipating member for dissipating heat generated by a semiconductor element (not shown). A ceramic substrate 2 supports the semiconductor element (not shown), and is patterned to connect the wiring of the semiconductor element with thin metal lines (not shown). A neck 3 is provided on the stud 1, and the ceramic substrate 2 is joined to the neck 3 with a brazing material 4 such as an Ag--Cu alloy.
In the conventional semiconductor package having the above-described construction, the neck 3 is made of a material, such as copper, having excellent thermal conductivity, and is formed into an integral structure with the copper stud 1. The ceramic substrate 2 is made of a material such as beryllia or alumina, and is patterned as desired for bonding of the semiconductor element, the metal thin lines, etc.
As stated before, the ceramic substrate 2 is joined to the copper stud 1 by brazing the substrate 2. However, these members greatly differ from each other in their coefficients of thermal expansion. While the coefficient of thermal expansion of the copper stud 1 is 17.times.10.sup.-6 /.degree. C., that of the ceramic substrate 2 is 7.6.times.10.sup.-6 /.degree. C. As a result, when, after the brazing, the copper stud 1 and the ceramic substrate 2 are cooled to room temperature, the ceramic substrate 2 is subjected to a large compressive force. The force causes the following problems. Cracks may start from the surface of joint between the substrate 2 and the stud 1. Thermal stress may remain within the ceramic substrate 2 and cause formation of micro-cracks at normal operation temperature. Such micro-cracks can lead to the formation of cracks.